1. Field of the Invention
The present invention relates to an electrophotographic photoconductor and an image-forming apparatus provided therewith. In particular, the present invention relates to an electrophotographic photoconductor, which is excellent in contamination resistance and is capable of preventing the generation of exposure memory for a long period, and an image-forming apparatus provided with such an electrophotographic photoconductor.
2. Description of Related Art
Heretofore, organic photoconductors have been widely used as electrophotographic photoconductors, which contains a charge-generating agent for generating electric charges by light exposure and a charge-transfer agent for-transfer the generated charges, and a binder resin for dispersing these substances therein to form a layered structure.
An image-forming apparatus using such an organic photoconductor employs an image-forming process by sequentially arranging means for charging the surface of the photoconductor, means for irradiating light on the charged surface to form a latent image, means for developing the latent image with toner to form a toner image, and means for transferring the toner image onto a sheet of printing paper.
In this process of an image formation, a device for neutralization of electricity by light irradiation is arranged. Such a device is responsible for erasing residual electric charges remained on the surface of the photoconductor after the image transfer. Therefore, even in the case of repetitive use, the process is allowed to prevent the generation of the so-called transfer memory or exposure memory by resetting residual potentials remained in previous cycles of use.
However, space charges can be generated in the inside of the photoconductor even though such a process is employed. When the photoconductor is repeatedly used, the space charges are accumulated in the photoconductor. Therefore, there is a problem in that desired image characteristics can not be constantly obtained.
To solve such a problem, a positively-charged mono-layer type electrophotographic photoconductor has been disclosed (see patent document 1, for example). In this photoconductor, as well as the use of a specific electron-transfer agent, a terphenyl compound is used as an additive. Thus, even when a reversal development system is employed, it allows the photoconductor to retain the transfer memory in a small amount and have an improved gas resistance against NOx, ozone, and so on.
Furthermore, there is disclosed in an electrophotographic photoconductor having the stability of electric characteristics thereof in positive charging in repetitive use (see patent document 2, for example).
However, even though the use of such a photoconductor can lead to improvements in transfer memory and repetition stability to some extent, there is another problem in that residual electric charges can be generated on a photosensitive layer after transfer. In addition, in the process of repetitively using the photoconductor in this way, when any of contaminant components from a human body or from a contacting portion of the photoconductor has attached on the surface of the photoconductor, cracks can occur from the contaminant-attached portion, thereby causing a lowering in image characteristics. Furthermore, these photoconductors require a process of erasing residual charges using means for neutralization of electricity as an image-forming system, so that there is a further problem in that it is difficult to cope with miniaturization of a device.
[patent document 1] JP-2001-242656 A (Claims)
[patent document 2] JP-2000-314969 A (Claims)